Safety workbenches fulfill various functions. They are used above all for protecting the operator from direct exposure to infectious aerosols, protecting the immediate laboratory surroundings from a contamination by released aerosols (environmental and personal protection), and protecting the product and the materials used from contamination by microorganisms from the surroundings.
The basic construction of safety workbenches comprises an inner chamber enclosed by a housing, which has a work opening on the housing front side, which is closable by a transparent front pane which is adjustable upward and/or downward. The inner chamber is also identified in the meaning of the present invention as a working chamber or a working inner chamber. Such safety workbenches are already known in greatly varying embodiments from the prior art, for example, from DE 44 41 784 A1, DE 102 17 903 C1, DE 297 23 636 U1, and DE 100 17 196 A1.
Furthermore, safety workbenches have a floor trough in the lower section of the working chamber. Floor troughs of this type terminate the working chamber on the bottom with a seal, capture substances seeping through the work plate, and are to prevent the substances from unintentionally escaping to the outside and contaminating the surroundings of the safety workbench. A floor trough of the prior art is described, for example, in DE 102 14 158 A1. The floor trough is shaped from a one-piece metal sheet and is accordingly single-walled.
For the safety workbenches, it is important above all that harmful substances or bacteria from the inner chamber of the workbench do not reach the room where it is installed under any circumstances. Protecting the operators and the environment is in the foreground. Safety workbenches in laboratories, in particular those which are suitable for microbiological work, therefore have to meet strict safety requirements. They have fans which generate directed air flows and guide these air flows via special filters, to remove particles or aerosols entrained in the air and not permit them to reach the operator or outside the safety workbench. Such a safety workbench is described, for example, in DE 10 2004 032 454 A1.
So-called personal protection in safety workbenches is achieved by suctioning outside air through the work opening into the working chamber of the safety workbench. As long as this external air flow is not obstructed and sufficient air is suctioned in, particles and aerosols may not reach the outside from the inner chamber of the safety workbench. The suctioned external air thus forms an air curtain flowing through the work opening, which protects the person working at the safety workbench and/or the environment from contamination by the particles. A pressure reduced in relation to the pressure in the surroundings of the safety workbench exists inside the working inner chamber of the safety workbench due to the flow guiding, which is also referred to as a partial vacuum in the following. The partial vacuum ends at the surface of the floor trough, which forms the lower terminus of the working inner chamber, facing toward the working chamber.
To ensure that no leaks arise in the area of the floor trough, corresponding model testing is typically absolutely required for the licensing of the safety workbench. However, this does not preclude that leaks will occur in the area of the floor trough in the course of use, which are possibly no longer recognized. This may represent a significant hazard to the operating personnel and the environment.